Bone health in facioscapulohumeral muscular dystrophy: A cross-sectional study

French National Protocol for diagnosis and care of facioscapulohumeral muscular dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common genetically inherited myopathies in adults. It is characterized by incomplete penetrance and variable expressivity. Typically, FSHD patients display asymmetric weakness of facial, scapular, and humeral muscles that may progress to other muscle groups, particularly the abdominal and lower limb muscles. Early-onset patients display more severe muscle weakness and atrophy, resulting in a higher frequency of associated skeletal abnormalities. In these patients, multisystem involvement, including respiratory, ocular, and auditory, is more frequent and severe and may include the central nervous system. Adult-onset FSHD patients may also display some degree of multisystem involvement which mainly remains subclinical. In 95% of cases, FSHD patients carry a pathogenic contraction of the D4Z4 repeat units (RUs) in the subtelomeric region of chromosome 4 (4q35), which leads to the expression of DUX4 retrogene, toxic for muscles (FSHD1). Five percent of patients display the same clinical phenotype in association with a mutation in the SMCHD1 gene located in chromosome 18, inducing epigenetic modifications of the 4q D4Z4 repeated region and expression of DUX4 retrogene. This review highlights the complexities and challenges of diagnosing and managing FSHD, underscoring the importance of standardized approaches for optimal patient outcomes. It emphasizes the critical role of multidisciplinary care in addressing the diverse manifestations of FSHD across different age groups, from skeletal abnormalities in early-onset cases to the often-subclinical multisystem involvement in adults. With no current cure, the focus on alleviating symptoms and slowing disease progression through coordinated care is paramount.

Cross-Sectional Study of Knee Bone Mineral Density and Fragility Fractures in Patients with Neurological Injuries and Neuromuscular Disorders

BACKGROUND

Patients with neurological injury and neuromuscular disorders are at increased risk for osteoporosis and fragility fracture. This cross-sectional study investigated whether knee bone mineral density (BMD) correlates with fragility fracture in patients with neurological injury and neuromuscular injuries.

METHODOLOGY

In this retrospective chart review, 435 participants underwent dual-energy X-ray absorptiometry (DXA) for BMD analysis. Distal femur and proximal tibial BMD measurements were performed as per the Toronto protocol. Spine, hip, and forearm DXA was performed following the standards of the International Society of Clinical Densitometry, 2019. Blinded and independent clinical evaluations and laboratory exams were performed. Participants were divided into groups with and without fracture confirmed by clinical history and radiography.

RESULTS

Distal femur and proximal tibial BMD were measured in 288/435 (66.2%) participants. Osteoporosis was noted in 138/288 (47.9%) patients. Fractures occurred in 95/435 participants (21.8%), including one fracture in 64/435 participants (14.7%), two fractures in 24/435 participants (5.5%), and greater than two fractures in 7/435 patients (1.6%). Fractures were noted in 23/54 (42.6%) participants with post-polio syndrome, 21/66 with brain injury (31.8%), 3/10 (30%) with brain injury and spinal cord injury, 24/98 (24.5%) with neuromuscular disorders, 9/52 (17.3%) with nontraumatic spinal cord injury, and 15/155 (9.7%) with traumatic spinal cord injury. The median BMD of the knee and hip was lower in participants with fractures. Distal femur and proximal tibial BMD (odds ratio [OR] = 0.02, 95% confidence interval [CI]: 0.01-0.45) remained independently associated with fragility fracture in multivariable analysis.

CONCLUSION

Proximal tibial and distal femur BMD measurements offered additional information on neurological injury and neuromuscular disorders.

Facioscapulohumeral Muscular Dystrophies

PURPOSE OF REVIEW

Facioscapulohumeral muscular dystrophy (FSHD) is a common muscular dystrophy affecting both pediatric and adult patients. This article reviews the phenotype and pathophysiology of the disease as well as the recent efforts in clinical outcome measures and clinical trials.

RECENT FINDINGS

As the name implies, FSHD involves weakness of facial muscles, muscles that fix the scapula, and muscles overlying the humerus (biceps and triceps). The distinctive phenotype of FSHD occurs secondary to two different genetic mechanisms. FSHD type 1 (FSHD1) is due to a deletion on chromosome 4q, leading to hypomethylation and derepression of DUX4. FSHD type 2 (FSHD2) is due to mutations in SMCHD1 with resulting hypomethylation of the same subtelomeric region of chromosome 4q and derepression of DUX4. Understanding the central role of DUX4 has opened up the possibility of disease-modifying treatments. In preparation for clinical trials of novel agents, researchers are in the process of validating a number of clinical trial outcome measures including MRI, the 6-minute walk test, the FSHD Composite Outcome Measure, reachable workspace, electrical impedance myography, and the FSHD Health Index.

SUMMARY

The treatment of FSHD is currently supportive only. While past clinical trials in FSHD have been largely disappointing, novel agents in development, including antisense oligonucleotides, gene therapy, and small molecules, hold promise for future meaningful therapies.

Targeting the Muscle-Bone Unit: Filling Two Needs with One Deed in the Treatment of Duchenne Muscular Dystrophy

PURPOSE OF REVIEW

In Duchenne muscular dystrophy (DMD), the progressive skeletal and cardiac muscle dysfunction and degeneration is accompanied by low bone mineral density and bone fragility. Glucocorticoids, which remain the standard of care for patients with DMD, increase the risk of developing osteoporosis. The scope of this review emphasizes the mutual cohesion and common signaling pathways between bone and skeletal muscle in DMD.

RECENT FINDINGS

The muscle-bone interactions involve bone-derived osteokines, muscle-derived myokines, and dual-origin cytokines that trigger common signaling pathways leading to fibrosis, inflammation, or protein synthesis/degradation. In particular, the triad RANK/RANKL/OPG including receptor activator of NF-kB (RANK), its ligand (RANKL), along with osteoprotegerin (OPG), regulates bone matrix modeling and remodeling pathways and contributes to muscle pathophysiology in DMD. This review discusses the importance of the muscle-bone unit in DMD and covers recent research aimed at determining the muscle-bone interactions that may eventually lead to the development of multifunctional and effective drugs for treating muscle and bone disorders regardless of the underlying genetic mutations in DMD.

What is the Fracture Risk in Patients at a Multidisciplinary Neuromuscular Clinic?

Many neuromuscular diseases (NMD) result in muscle weakness, immobility and greater fracture risk. The objective of this study is to determine the fracture risk of adult patients at a multidisciplinary NMD clinic. Fracture risk was calculated using the Fracture Risk Assessment Tool, the presence of osteoporosis was quantified using bone densitometry and contributing co-morbidities were screened through serum markers. Of the 36 patients studied, 47% were found to be of moderate and high fracture risk. Two thirds of these patients had not been previously screened or treated for osteoporosis. These findings suggest that NMD patients warrant routine screening for osteoporosis and early treatment to reduce fragility fracture.